Telemetric device



TRANSMITTER Aug. l14, 1945.

TELEMETRIC DEVICE Filed Feb. 17, 1944 13 Sheets-Sheet 1 Augrulfl, 1494.5. o. R. MILLER TELEMETRIC DEVICE Filed Feb. 17, 1944 15 Sheets-Sheet 2 /A/l/ENTOR 0. R. M/LL E R DV Ns,

ATTORNEY Aug. 14, 1945. o. R. MILLER 2,381,920

TELEMETRIC DEVICE Filed Feb. 17, 1944` 13 Sheets-Sheet 3 HARK/N6 SIGNAL 05 C /LLATOR lll-1- QAM/LER BV ATTORNEY Aug. 14, 1945. o. R. MILLER 2,381,920

l TELEMETRIC DEVICE Filed Feb. 17. 1944 13 sheets-sheet 4 f-aa /o Puur/64 COUNTER TENS HUA/0R50:

THOUSANDS /MPULSE GEN PHASE FILTER /N VEN TOR o. M/4 L ER ATTORNEY [TEA/THOUSANDS Aug. 14, 1945. 0, R MlLLER 2,381,920

TELEMETRIC DEVICE Filed Feb. 17. 1944 13 Sheets-Sheet 5 /M/ENTOR y 0. R. MILL E R All@ 14 1945 o. R. MILLER TELEMETRIC DEVICE v 13 Sheets-Sheet 6 Filed Feb. 17, 1944 /NVENTOR O. R. MIL L ER Elson .#351 n Aug. 14, v(1945. o. R. MILLERy 02,381,920

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,N s n lill-II' /NVENTOR By ORM/LER 13 Sheets-Sheet 11 /A/1/5/1/T0RA 0.R. M/LL E R By ATTORNEY O. R. MILLER TELEMETRIC DEVICE Filed Feb. 17, 1944 Aug. 14, 1945.

y Aug. 14, 1945'. o. R. MILLER TELEMETRIC DEVICE n Filed Feb. 17, 1944 13 Sheets-Sheet 12 /Nl/ENTOR 0. R. MILL E R B V l Z ATTORNEY U8 .14 1945 o. R. MILLER TELEMETRIC DEVICE Filed Feb. '17, 1944 15 Sheets-Sheet 13 MAAA N\ ...ut

/Nl/ENTOR O. R. M/L L ER ATTORNEY l specific example thereof it is Patented Aug. 14, 1945 I UNITED sTATEs PATENT- ori-icE Ghmer R.

Bell Telephone Miller, Morristown, N. J., assigner to Laboratories, Incorporated, New

York, N. Y., a corporation of New York Application February 17, 1944, Serial No. 522,713

3 Claims.

This invention relates to telemetric devices and particularly to number indicators, the object of the invention being to provide means controllable from some control point to continuously display at one or more distant points a plurality of numbers and to cause instant change ln such displays when the controls at the central point are changed.

vIn accordance with this invention and as a desired to post at one or more remote locations three live-digit numbers and to cause instant change in such displays under control of an operator at a central location. The operation is carried out over a single conductor transmission channel by'electronic devices similar in general principle to those devices known as cosmic ray counters, which are 'capable of very high speed operation. The apparatus employed may be termied an electronic commutator-since the operation is similar in action to a pair of rotary distributors which simultaneously connects a transmitting circuit to a corresponding receiving circuit for a short interval of time and thus distributes the use of a single transmission channel over a large number of pairs of complementary terminal circuits. But unlike the conventional rotary distribution, the arrangement is very high speed and is limited only by the transmissioncharacteristics of the channel. Thus the link between the two corresponding ends of a circuit. even where there are one hundred and fty or more such complementary pairs may be completed a great many times per second.

Where circuit conditions can be rigidly controlled so that no unwanted disturbances will occur to throw the receiving arrangement out of synchronism with the transmitting arrangement a straight and permanent connection between the two ends may be made. However since these devices are extremely sensitive and responsive to very weak impulses and the system is likely to be used where great mechanical disturbances and vibrations which might result in unwanted electrical disturbances in the apparatus may occur, an arrangement somewhat analogous to the startstop arrangements used in certain types of mechanical rotary distribution systems may be employed. Thus the transmitting arrangement as well ras the receiving arrangement consists of an electronic counting device responsive'to a continuous train of impulses and if one of the arrangements misses an impulse. or responds to a stray impulse the synchronous action of the two arrangements will be disturbed. In such a case the response of the receiving device will be in error. Hence a synchronizing signal is transmitted periodically which has the eiect of stopping the action of the receiving arrangement when it has gone through its cycle of operations and reached a normal position. The receiving arrangement is then rendered unresponsive to incoming signals until the transmitting arrangement reaches its corresponding normal position whereupon the two arrangements at the opposite ends of the transmission channel take up their synchronous operation.

In accordancewith the specific embodiment of the invention disclosed herein the transmitting arrangement consists of three groups of counting tubes functioning to scan the electrical condition of the transmitting decade points to determine and transmit' a signal for a particular digit for each of the three number designations in turn. For this purpose of tubes has a complete cycle of ten different circuit conditions continuously responsive to a source of regularly recurring impulses, the second group of tubes has a complete cycle of iive different circuit conditions continuously responsive to the recurring completion of its cycle by the rst group and the third group of tubes has a complete cycle of three different circuit conditions continuously responsive to the recurring completion of its cycle by the second group.

At the receiving end a similar arrangement of tubes is employed to distribute the timed signals to operate corresponding indicators.

The synchronizing means comprises an extra set of counting tubes at each end of the transmission channel which interrupts the ilow of impulses into the principal counting arrangements for one pulse and thus effectively renders the complete cycle equal to one hundred and fiftyone impulses. During the interval between the one hundred and fiftieth impulse and the one hundred and fifty-mst impulse a synchronizing signal is transmitted. At the receiving end, if the arrangements at the two ends are in synchronism, this synchronizing signal acts to continue uninterruptedly the operation of the receiving arrangement. If for some reason the receiving device has fallen one impulse period behind the transmitting arrangement then the action of the receiving arrangement is held up for the next one` hundred and fifty impulses until the transmitting yarrangement goes through an almost complete cycle of operations, the signals sent during this nearly complete cycle being ineffective at the receiving end. If for some reason the first group the transmitting device has fallen one impulse period behind the receiving arrangement.4 then the action of the receiving arrangement is held up for only a single impulse period. In any case erroneous operation of the indicators at the receiving end can only take place during a small fraction of a second so that the effect will appear as a flicker (the indicators being in the form of glow lamps) persistingfor too short a period to give erroneous information. y

The transmission channel carries both the alternating current used to derive the driving impulses and the information signals. Since this alternating current is of comparatively low frequency and the information signals are of compamtively high frequency it is a simple matter to lter these currents out at the receiving end and to direct them each into the circuits in which they become useful.

A feature of the invention is the use of a pair of similar electronic counters to perform the functions of rotary distributors at either end of a transmission channel.

Another feature is the use of a single source of alternating current for driving th'e two electronic counters, the said alternating current being transmitted over the same channel simultaneously with the mark signals transmitted when the counters couple a marked transmitting termination with its corresponding receiving termination.

Another feature is a synchronizing arrangement for the counters consisting of electronic means in each for stopping the response thereof to the driving source at the end oi' each' complete cycle of operations. At the transmitting end means is provided to send out a start signal and immediately recondition the counter so that invariably such counter is halted only for a single impulse. At the receiving end the incoming start signal will only be enective ii' the receiving coun- -ter has simultaneously reached a similar position. If as hereinbefore pointed out the receiving counter has fallen one or more steps behind th'e transmitting counter, then the receiving counter is held out of operation for nearly a complete cycle, until the transmitting counter again catches up'? with the receiving counter.

Another feature is the use of different frequency currents for driving the counters, for sending mark signals and for sending start signals with f filtering means at the receiving end for diverting these diierent frequency currents each into its own useful ch'annel.

Other features will appear hereinaftr.

The drawings consist of thirteen sheets having seventeen figures, as follows:

Fig. 1 shows how Figs. 3 to 8, inclusive, may be placed to form a complete circuit diagram;

Fig. 2 is a schematic circuit diagram to explain the theory of operation of the system shown in Figs. 3 to 8:

Fig. 3 is a circuit diagram, partly schematic, of the transmitting end of the system and sh'owing in full the circuit of one number transmitter;

Fig. 4 is an extension of the circuits of Fig. 3, indicating by blocks the circuits of two other number transmitters and showing in full certain other common circuit details;

Fig. 5 is a circuit diagram, partly schematic, showing part of the receiving circuits at the distant end of the line, showing in full the circuits of the units indicator and indicating by blocks the tens, hundreds and thousands indicators;

Fig. 6 is an extension of Fig. 5 and shows in full the circuit of the ten thousands indicator,

and indicates by blocks .two other number indicators each having like units, tens, hundreds,

.thousands and ten thousands indicators, and in addition shows certain other common circuits in some detail;

Figs. '7 and 8 are extensions of Figs. 5 and 6, respectively. showing Dart of the details of the circuits of the units and ten thousands indicators of the ilrst number indicator;

. Figs. 9 and 10 when placed with Fig. 9 to the left of Fig. 10, show circuit details of a start-stop feature which may be employed to insure accuracy in the operation of the system, Fig. 9 showing circuit details at the transmitting end and Fig. 10 showing circuit details at the receiving end of the transmission line;

Figs. 1l, l2'and 13, respectively, show circuit details of th'e common leads from the ten-impulse counter, the live-impulse counter and the threeimpulse counter;

Fig. 14 shows the circuit details of a ten-impulse counter; 1

Fig. 15 shows the circuit details of a five-impulse counter Fig. 16 shows the circuit details of a threeimpulse counter: and

Fig. 17 shows the circuit details of an impulse generator.

'I'he operation of the system of the present invention may be readily understood by the following description of the theoretical circuit of Fig. 2'. The system consists essentially of a pair of synchronous distributors connected by a transmission line I. The transmitting distributor consists of an arm 2 driven continuously over a bank of one hundred'and nity-one contacts bythe motor 3.

' The receiving distributor consists of alike arm d driven continuously over a bank of one hundred and fty-one contacts by the motor 5. The motors 3 and 5 may be synchronous motors both driven from a common source 6 of alternating current, whereby the arms 2 and 4 may be rotated in synchronism.

If there is any possibility that the arms 2 and 4 may fall out of step with each other or for purposes of achieving synchronism between these arms, a start-stop feature may be added. This is indicated by the connections to the one hundred and fifty-first contact in each bank. At the trans. mitting end this will consist of a ground connection tothe said contact and at the receiving end it will consist of a magnet 1 connected to the corresponding contact. Such magnet 1 is provided with an armature which in its normal position will stop the rotation of the arm 4. Therefore if the arms 2 and 4 are in synchronism with each other the magnet 1 will be energized once during each revolution of the arms 2 and 4 and the armature of magnet 1fwill be moved to a point where the free movement of arm 4 is unhindered. If the arms 2 and 4 should fall out of step with each other then through the non-energization of the magnet 1, the arm 4 will come to rest on its one hundred and fifty-first contact and will remain there until the arm 2 is moved to a corresponding position, whereupon the magnet 1 will be ener` gzed and the arm 4 will be mechanically connected to the motor 5 and will thereafter rotate in synchronism with the arm 2. Arrangements of this nature are well known in the art. Other arrangements are known which allow faster rotating speeds but this is analogous to the hereinafterdescribed electronic commutator.

At the transmitting end the one hundred and fifty contacts over which the arm 2 travels are connected to corresponding contacts of fifteen switches each controlling the connection of battery to ten contacts and arranged so that three rive-digit numbers may be set up on the said switches. Thus the switch arm l may be set on its seventh contact which is connected to the one hundred and thirty-seventh contact traversed by the distributor arm- 2. The switch arm 8 is indicated in the drawings as controlling the thousands digit of the third number. An inspection of the other switch arms will show them to be set, by way of example, to transmit the numbers 31261, 59719 and 17921, respectively.

At the receiving end of the transmission line there are fifteen number indicators each consisting of a bank of ten indicators which may be lamps or other mechanical yindicators having visual persistence or slow-releasing properties suillc'ent to give a constant indication when they are repeatedly energized once during each revolution of the arm 4. Thus the seventh indicator in the thousands group of the third number is shown connected to the one hundred and thirty-seventh contact traversed by the arm 4, so that once during each revolution of the arms 2 and 4 a circuit will be completed between battery, resistance i8, switch arm 8, distributor arm 2, transmission line I, distributor arm 4, indic-ator 9 to ground. In this case only the seventh indicator in the thousands group in the third number will be energized, and likewise only one indicator in each of the other groups of indicators will be energized, whereby the numbers 31261, 59719 and 1792-1 will be displayed.

The switch arms such as 8 may be reset at any time and since the arms 2 and 4 travel at a relatively high speed the numbers displayed at the receiving end will appear to be instantly changed. Thus the display of numbers may be constantly in accordance with the'setting of the tranmitting device.

It should be noted that a plurality of receiving devices may be connected in multiple so that the nformation set up by the switch arms such as 8 nay be constantly transmitted to and displayed at a plurality of different locations.

The system of the present invention operates in the manner above set forth excepting that no mechanically moving parts are employed other than the manually controlled decade transmittingr switches. As shown in Figs. 3 to 8, a source of alternating current il is used to energize certain counting tube combinations both at the transmitting end and the receiving end of the transmission line I2, being connected to the transmission line through a conventional driver amplifier i3 whereby current therefrom is transmitted over the transmission line simultaneously with the signaling impulses produced by the transmitter. In the transmitter circuit the current from the driver oscillator II operates an impulse generator I4 to produce a constant stream of impulses'recurring at the frequency of the source I I and suitable to operate a tube counter. These impulses are counted by a ten-impulse counter I5 repeatedly, this device energizing each of the ten conductors i6 in turn repeatedly. For each ten impulses counted by the device I5 one impulse is transmtted to the five-impulse counter i1 which in a similar manner energizes each of the five conductors i8. For each live impulses counted by the device I1 one impulse is transmitted to the threeimpulse counter I3 which in a similar manner energizes each of the three conductors 28. Where, by way of example, a combination of three conductors is found simultaneously energized, as conductors 2i, 22 and 23, then a signalis sent out over the transmission line I2. Since the five conductors in the group i 8 are energized in turn then the tubes 24, 28, 28, 21 and 28 are in turn conditioned to be affected by the conditions found in the group i8 as determined by the setting of the decade switches 29, 2li. 3|, 32 and 33. respectively. Thus an impulse will be sent out somewhere within each group of ten impulses counted.

In a similar manner, since the three conductors in the group 20 are energized in turn, then the tube 35 in the first number transmitter and the corresponding tubes in the vother two number transmitters will in turn be conditioned to be affected by the tube 34 and the corresponding tubes in the other number transmitters. Each time, therefore, that three such conductors as 2i, 22 and 23 are simultaneously energized the tube 38 will be affected and the gate relay 31 will allow an impulse from the oscillator 38 to be transmitted through the marking amplifier 38 to the transmission line I2. Thus in a complete cycle the ten-impulse counter I5 will go through fifteen complete cycles, the five-impulse counter will go through live completek cycles and the three-impulse counter will go through one complete cycle and fifteen signals will be transmitted.

As will be explained more in detail hereinafter, each of the conductors in the group I8 is normally held at a comparatively high positive potential, and likewise each ofthe conductors in the group I8 is normally held at a comparatively high positive potential. A negative battery is connected through a resistance 40 to the grid of tube 24 and since this grid is also connected through resistance 4I to some one of the conductors in group I6 and through resistance 42 to a particular one (22) of the conductors in group I8, the grid is thus connected to the potentiometer point at which the potential is such as to render the tube 24 normally conducting. Only when the p0- tentials communicatedthrough the resistances 4I and 42 are simultaneously at a. comparatively low positive potential does the potential of the said potentiometer point, and hence the grid of tube 24, fall to such a value that tube 24 becomes non-conducting. The anode of tube 24 is connected to a potentiometer point between resistors 43 and 44 and hence when tube 24 becomes nonconducting the potential of this point is raised from a normal comparatively low positive potential. Consequently the potentiometer point between resistances 44 and 45 shows a rise in potential at this time so that tube 34 which is normally non-conducting now becomes conducting. This causes the `potentiometer point between resistances 46 and 41 to fall and likewise the potentiometer point between resistances 41 and 48 to fall. However, it isnot until. the 'normally comparatively high positive potential of the conductor 2i in group 20 connected to resistance 48 also falls to a comparatively low positive potential, that the potential of the potentiometer point between resistances 48 and 41, 'which is connected to the grid of tube 35 will fall to a value sufiicient to cause the tube 35 to become non-conducting. Thus when conductors 2|, 22and the conductor now connected to switch arm 29 simultaneously fall to a comparatively low positive potential, tube 35 will respond by becoming non-conducting.

Resistances 49, 50 and 5I constitute a potentiometer. When tube 35 is in a non-conducting state the potentiometer point between resistances 50 and 5I is at a comparatively high positive pothe corresponding tubes connected to resistances I! and I8 is the same. the grid of the lower triode combination of tube It is at a comparatively low positive potential and this lower triode combina tion is in a non-conducting state. However, when any one oi' the tubes such as ll becomes nonconducting then the grid il rises to a sumciently high positive potential to render this lower triode combination conducting.

'Ihe grid of the upper triode combination of tube is connected to a potentiometer point between resistances I4 and 55' and also to the anode of the lower triode combination. Consequently as the lower triode combination becomes conducting (on receipt of a signal) the grid of the upper triode combination falls to a comparatively low positive potential and the upper triode combination becomes non-conducting. Thus the lower and upper triode combinations are always opposed in state and the upper triode combination is non-conducting during the transmission of a signal.

The anode of the upper triode combination of tube It is connected to a potentiometer point between resistances 58 and I1 and the screen grid of tube 31 is connected to a potentiometer point between resistances 51 and il. Consequently when a signal is to be transmitted the screen grid of gate tube 31 rises in potential and allows the output of the oscillator Il to so affect the grid f this tube that a corresponding signal is produced in the anode circuit thereof. This signal is therefore in the form of a timed transmission of alternating current of the frequency of the source ll transmitted to the marking amplifier 3l and thence out over the transmission line I2.

It is thus apparent how the signals corresponding to the digits 31261, 59719 and 17921 are sequentially transmitted.

At the receiving end of the transmission line I! a pair of filters 60 and Il are provided. Filter Il is designed to pass current from the driver oscillator Il and-thus provide a source of.cur rent for operating the impulse generator il. A phase adjusting circuit I3 is provided so that the impulses from the generator may be brought into exact synchronism with the impulses from the-transmitting generator I4. These impulses will then operate a ten-impulse counter Il similar to the ten-impulse counter IS, a uve-impulse counter 65 similar to the five-impulse counter I1 and a three-impulse counter similar to the low positive potential by the use of an inverter tube placed in the lead from the ten-impulse counter. Thus the normally high potential (nrst left) lead from the ten-impulse counter 84 goes to the grid of tube. and holds this in a normally conducting state. Therefore the potential on conductor 1| is normally comparatively low, and hence the potentiometer point between resistors 12 and 13 is normally low so that the glow tube 15 is prevented from operating. 0nly when the potential on conductor 1| leading through resistance 12 and the potential on conductor 18 leading through resistance 1I are simultaneously comparatively high is the control tential. Since the normal state of tubo ll and.

electrode of tube 1l raised sumclently to nre the tube and to make it glow for visual indica purposes. Each of the leads from the ten pulse counter 04 has an inverter tube such as 10 inserted betwen it and the corresponding conductor in the group 01. kas indicated by the broken lines just below the ten-impulse counter I4 The potential of conductor 1l is controlled from the uve-impulse counter li. Each of the conductors in group Il is normally at a comparatively high positive potential so that the potentiometer pointbetweenresistances 11 and 1t) (conductor l0 as will hereinafter appear also being normally at a comparatively high positive potential) will be sufiiciently high to render the tube 8| conducting. With this tube conducting its anode isthen at a compartively low potential. Therefore when conductors 82 and 80 simultaneously fall in potential tube 8| will become nonconducting and consequently conductor 19 will rise in potential. If during such a period conductor 1| also rises in potential, tube 1I will be triggered oi! and will glow, the tube thereby functioning as an indicator. A tube suitable for such a use is disclosed in Patent 2,271,685 1f to B. O. Ekstrand, February 3, 1942.

The potential of conductor 80 is controlled by tube I3, so that as tube 83 is in a conducting or non-conducting state its anode is at a comparatively low or comparatively high positive potential. Tube Il is controlled by the condition of a conductor in group 69 and by the incoming signal which appears as a positive pulse on conductor 84. 'I'he normal condition of the three conductors coming from the three-pulse counter is a comparatively high positive potential whereby the tube Il by way of example is rendered conducting thus holding its anode at a comparatively low positive potential. Thus through resistance 89 the grid of tube 93 is held normally low and tube 8l is rendered non-conducting to hold its anode and consequently conductor 80 normally high. Also.' as will appear hereinafter, the potential of the grid of tube $3 is also held normally low by the potential of conductor 84 as connected to the grid of tube 83 by resistance 81.

Now it will be realized that one of the three conductors coming from the three-pulse counter is brought down to a low potential during the period when the corresponding number indicator is to be rendered active. Thus when the number indicator shown by the details oi' the umts indicator and the broken line rectangles 8l, 89 and 90 representing the tens, hundreds and thousands indicators, respectively, in Fig. 5 and the details of the ten thousands indicator in Fig. 6 are to be rendered active, the potential of the grid of tube 85 will be lowered and the other two conductors coming from the three-impulse counter IB will rise in potential. Thus the potential of the grid of tube 83 is conditioned by a rise in potential through resistance 86 so that when a signal comes in over conductor 84 the tube Il Will become conducting, the potential of conductor 80 will be lowered and-.if the potential of conductor 82 is now lowered tube 8| Will become non-conducting to pass the signal on as a rise in potential on conductor 16. Since at this time conductor 9| is at a comparatively low potential tube 92 will be non-conducting and the anode thereof will be at a comparatively high potential. Conductor 93 is connected to the upper electrodes of all the glow tubes such as 15 and hence during this period all such tubes of one number indicator are conditioned to operate when, as explained, the potentials supplied through resistances such as412 and 14 become simultaneously high.

The incoming signal as hereinbefore explained is in the form of a short application of a particular frequency alternating current` which is passed by the filter 9|. This signal is then ampliiled by a conventional and appropriate amplifier 94 and passed to the grid of tube 95 which becomes conducting and consequently operates to lower the potential of its anode during the period of. the reception of the signal. Tube 95 thus actsas a detector and translates a pulse consisting of a plurality of cycles of alternating current into a single impulse consisting of an interval during which the anode of tube 95 is lowered in potential. Tube 96 has its grid connected to a potentiometer point between resistances 91 and 99 controlled vby the tube 95 and therefore it responds to this signal by becoming non-conducting, thus translating the signal to an impulse of comparatively high positive potential on conductor 84 with the results hereinbefore explained. Thus it will be seenhow the sequentially arriving signals are translated into a display of the numbers 3126i, 59719 and 17921. Since the frequency of the source I may be comparatively high-the number of times the complete'cycle of operations may be completed per second may be so high that the display of the numbers may be altered apparently as the switches 29 to 33 and so on are being altered, thus producing at one or more receiving stations a continuous and instantaneously azustable display of certain infomation.

Attention is directed `to the arrangement of the conductors in the group 69 coming from the three-impulse counter 66. These conductors are affected in rotation, that is, while the first (counting-from the left) is at a comparatively high positive potential, the second-and the third are lat a comparatively low positive potential. 'Ihus while the rst number display circuit is enabled by the comparatively high positive potential supplied by way of resistor 06 the conductor 99 is rendered active by its connection through the tube 92 to the third conductor. 'I'hus when one of the tubes such as 15 is triggered oft it remains active as long as conductor 93 remains active. This is for the period of the setting of v the first and the second number display indicators,for when the setting of the first is completed, although the first conductor of the group 69 changes from high to low potential and the second thereupon changes from low to high potential, there is no change in the third conductor until the third number indicator is to be rendered active. triggered off remains aglow for a period between one-third and two-thirds of the time taken for a complete cycle, depending on whether it was triggered oil.' near the end or near the beginning of the count for the indicator in which it is situv ated. For this reason partly the display will ap- 'I'hus a glow tube after beingl 5, respectively, the one representing the circuits at the transmitting end and the other representing the circuits at the receiving end. In order to explain the start-stop feature, reference may be had to Figs. 9 and 10 placed end to end with Fig. 9 to the left of Fig. 10. I

At the transmitting end, shown in Fig. 9, the driver oscillator and the -impulse generator shown in Fig. 3 are used. In this case the detail circuits show the apparatus indicated by the rectangle l00 of Fig. 3. Here the output of the impulse generator in the form of a stream of positive impulses feeds into the tube |02 which pro duces a stream of negative impulses and this in turn is changed by the inverter tube |03 into a stream of positive impulses feeding into the tenimpulsecounter l5, the five-impulse counter I1 and the three-impulse counter I9. These function as hereinbefore described to operate the number transmitter here indicated by the rectangle |04 which in turn produces the marking signais which it transmits over the conductor |05 andl thence through the mixer amplifier |09 to the transmission line |01. On the one hundred and. iftieth count the three-impulse counter I9 transmits a negative impulse over conductor |08 which will reverse the state of the tubes |09 and I|0. Normally tube |09 is conducting and tube I|0 is non-conducting whereby the potentiometer point between the resistances and H2 .is at a comparatively high positive potential and whereby the other potentiometer point between the resistances ||2 and I I3 is at a comparatively' high positive potential, suilicient to render tube |02 conducting to pass the output of the generator I4 to the ten-impulse counter I5. When the negative impulse is transmitted to the suppressor grid of tube |09, this tube becomes non-conducteing and since its anode is thereby raised to a comparatively high positive potential and since this anode is connected to the screen grid of tube H0, tube ||0 now becomes conducting. As a result, the screen grid of tube |02 is lowered in potential to the point where it will no longer pass the impulses from the generator I4 to the tenimpulse lcounter l5 so that the one hundred and fifty-mst impulse does not reach the counter I5 to be counted.

When the tube |09 becomes non-conducting the potential of its anode which is connected to a potentiometer point between the resistors ||9 and I9 rises from a comparatively low to a com- .paratively high positive potential. The potentiometer point between the resistors II9 and |20 likewise rises and since this point is connected to the screengrid of tube I2l, tube |2| becomes conducting and passes current from the source |22 to the conductor |23, which acts as a stop signal and is transmitted through the mixer amplifier |06 to the transmission line |01. It may be noted at this point that the current from the source |22 is of a different frequency from other signals being passed over the transmission line so that it may be properly filtered at the distant end and thereby directed in its proper channel for purposes which will be presently described.

When tube 09 becomes non-conducting and the negative impulse which produces this condition has terminated, tube Il 0 becomes conducting as described. The comparatively highpositive potential of the anode of tube |09 now affects the potentiometer points between resistors IIB and |24 and between |24 and |25 as a consequence of which the potential `of the screen grid oftube |23` rises and this tube becomes conducting. The next or one hundred and fifty-first impulse in the series transmitted from the generator i4, therefore, is conducted through tube |23 so that the potential of its anode suddenly drops thus producing a negative impulse to the suppressor grid of tube which reduces this tube to a non-conducting state, which in turn activates tube |02 to pass the next, or first of a new series of impulses on to the counters. The movement of -tube ||0 to the non-conducting state also causes tube |03 -to conduct whereby the tube |2| is rendered non-conducting and the transmission of current from the source |22 is stopped.

Thus by the arrangement shown in Fig. 9, each time after one hundred and fifty pulses have been counted by the counters l5, I1 and i3,

the transmission of impulses from the generator I4 to the counters is stopped for the time of one impulse and during this period a start signal is transmitted over the line |01. y At .the receiving end of the transmission line |01 there are provided the driver filter, the phase adjusting device 62 'and the impulse generator 03. The impulses from this generator, in the form of a stream of positive pulses, are passed by the tube |23, when active, to the grid of inverter tube |21. Each impulse passed by the tube |21 appears as a sudden drop of potential on the anode of tube |20 and therefore constitutes a negative impulse on the grid of inverter tube |21. This renders the tube |21 non-conducting for an instant so that the consequent s .udden rise of potential on its anode constitutes a positive ypulse to the impulse. counters here indicated by the rectangle |28 designated impulse counter. The impulse counter in. conjunction with the number indicator control |29 also controlled through the marking filter 8| performs the functions hereinbeiore described.

A conductor |30 leads from the impulse counter |28 and over this lead a negative impulse is transmitted on the one hundred and iiftieth count. Here tubes |3| and |32 are arranged as a pair, one of which is in a conducting state while the other is non-conducting. Normally tube |3| will be conducting so that the negative impulse transmitted over conductor |30 to the screen grid of tube |3| will reduce this tube to a non-conducting state. .Thereupon in a manner similar to that hereinbefore described, tube |32 which was heretofore non-conducting now becomes conducting. Therefore, the negative impulse over conductor |30 causes a reversal inthe condition -of Itubes |3| and |32. Tube |32 has its anode connected to a potentiometer point between resistors |31 and |38 and therefore causes the normally comparatively high positive potential thereat to be reduced to a comparatively low positive potential whereby the potential atL the potentiometer point between resistors |38 and |39 is lowered suillciently to prevent the further passage of impulses through the tube |26. There- 2,ss1,9ao

dition to pass impulses `so that `a. positive impulse from the generator (the one hundred and fiftyfirst impulse) will appear as a sudden drop in potential on the anode of tube |43. However the normal potential of the potentiometer point between resistances |33 and |34 is comparatively low so that the cathode of diode |44 is at a comparatively low potential whereby the grid of tube|43 is held down to a point where tube |43 will not be aiiected by a positive impulse from generator 33. However if the start signal is present from theone hundred and ftieth to the one hundred and mty-nrstmpulse the potential, as will be hereinafter described, oi the anode of tube 5I will be high which raises .the potential oi the anode of diode |44. Therefore the grid of tube |43 will be anected by' the positive impulse from generator 33.

The incoming start impulse, in the form of a short application of a particular frequency alternating current. will pass through the start filter appears as a positive potential on the cathode of the diode |44 and thus allows the one hundred and fifty-first (or any other positive) impulse from the generator 03 to eilect tube |43. Therefore, if .the start signal arrives simultaneously with the production of the4 one hundred and fifty-first impulse from the generator 63 the anode of tube |43 will produce a suiciently fore, tube |26 will not pass the one hundred and powerful enough negative impulse on the sup-- pressor grid of tube |32 to cause this tube to become non-conducting. Y

As .tube |32 is reduced to the non-conducting state, its anode will rise in potential and enable the tube |23 to pass the next impulse from the generator through the tube |21 to the impulse counter |28; Thereafter, .tubes |23, |3|, |32 and |43 remain as they are now (|23 and |3| conducting and |43 and |32 non-conducting) until another negative impulse is transmitted over the conductor |30 after lthe impulse counter has counted off one hundred and fty impulses.

It may be notedthat if the arrangement at the receiving end falls out of step with the arrangement at the transmitting end so that the start impulse does not arrive on the next pulse after tube |43 has become conducting, tubes |43 and |32 will remain active until such a start impulse is received, at which time a reversal will take place as described and .tubes |26 and |3| will become active to enable the impulse counter |28. Thus the circuit ceases to operate when the impulse counter reaches the count of one hundred and iifty and remains inertuntil another start impulse is received. If, during one cycle, the impulse counter should fail to count every impulse and should lose one by way of example, that is if it should fall one step behind the transmitter, the start impulse would arrive as the receiver `is counting the one hundred and iiftieth impulse but the start impulse at that time would be ineffective and so the receiver would wait without operating until the next start impulse is received. 'I'hus the circuit will autoassenso matically be resynchronized within one full cycle which taking only a small part of a second will cause nno'ticeable disturbance in the display of the transmitted numbers.

The impulse generator shown in Fig. 17 is a device which produces a single sharply defined impulse from each cycle of alternating current fed thereinto. Through means provided, this single sharply defined pulse may be made to occur at any particular point in the cycle over agiven range, as, for instance, just as the wave passes through zero from the positive half wave to the negative half wave. Thesourceof alternating current |68 may be the driver loscillator vof Fig. 3. Alternating current from this source flows through condenser |16| and thence `through the primary windingV of transformer `|62 to ground. The secondary winding of transformer` |82 thus becomes a source of alternating current to affect the triode |63. The cathode grid circuit of this tube may be traced from the cathode through resistance |64, the secondary winding .of the transformer |62, resistance |66 to the grid of tube |63. A condenser |66 is in parallel with both the resistance |=64 and a source of negative biasing potential comprising the resistance |61 and the well-known network of rectifiers |68,- |66, and |1|, energized yby a source of alternating current |12 and an interposed-'transformer |13. The potential supplied by this network is suicient to produce a given anode-cathode current flow in the tube |63 between the battery connected to lthe anode thereof and the resistances |14 and |16 to ground. Undenthese conditions, a given potential thus stands on the stehts cf this circuit this impulse may `icc made to appear with regularity at any point between near zero to maximum negative value in the incoming cycle from the source |66.

Fig. 14 shows a ten-impulse counter. This as well as the five and the three-impulse counter is y based on the action of .a plurality of pairs of cathode cf tube |53, this being c point cn thc l potentiometer consisting of the internal resistance of the tube and the two resistances |14 and Now. as an alternating current wavev in the secondary winding of transformer |62 rises from a zero value to an increasing positive potential,

the grid ofthe tube |63v becomes less negative and as a consequence the anode-cathode current increases. Therefore, the potential of the cathode with respect to ground increases so that the potential between the resistances |14 and |16 in time rises to a point where tube |11 will function. V

Normally :the cathode of tube |63 is connected in a. circuit with the elements of the diode |11,

resistance |18, condenser |19, resistance |16 to ground, whereby Athe condenser |19 may be charged as the potential of tube |63 rises. Therefore on the risingrpart of the positive half wave condenser |19 will be charged, but not to lthe full extent possible because While its upper terminal is rising, its lower terminal is also rising. In time the rising par-t of the positive half wave will reach its limit and thereafter the potential of the cath-- ode of tube |=63 andlikewise the potential of the potentiometer point betweenresistances |14 and |16 will decrease. The potential on the condenser |18 will remain at the highest point reached, due to the diode |11 but'l the lower terminal will decrease thus still further increasing the difference in potential set upon condenser |19. When the potential of the cathode of tube |16 yfalls'so that the grid bias reaches a critical value then the gas-filled tube |16 will fire and cause condenser |18 to discharge through the primary of transformer |86. This produces a current in the secondary which appears on the output conductor 8| as a positive impulse.

Through the proper` proportioning of the concounting tubes, only one of which will be described in detail herein. 'I'he tubes |86 and .|86 form such a lcounting pair, one of which is always energized and in a conducting state; The principle of operation is fundamentally the same as that of the well-known Eccles and Jordan circuit, disclosed in British Patent 148,582. These tubes are, however, pentodes with the anode of each connected to the screen grid of the other. When a negative impulse is applied to the suppressor grid of both. the combination of the two tubes reaches an extremely unstable state as the conducting tube decreases .to the non-conducting stage. This is caused by a charge on condenser |81 connected between the cathodes of the two tubes which is charged in one direction while tube |86 is active, and in the other direction 4while tube |86 is active. When the negative impulse is applied to the two suppressor grids, the discharge rate of condenser |81 through resistors |88 and |89 is slower than the rate of decrease of current through-the conducting tube due to the sharp negative impulse so there is a slight residual charge left, the magnitude of which depends on the rate of change or sharpness of the said negative pulse. Without condenser |81 the inherent differences between the two tubes would determine which one was to become active on recovery, and generally there is enough difference between even the most carefully matched pair to dictate thata certain one would invariably become conducting at this time. However, with condenser |81 connected as shown there is suillcient influence to overcome the inherent differences in even a badly matched pair. Now the fact is that upon recovery 'and with condenser |81 still holding a small residual charge, tube |86 will become active if tube |86 had been active before or tube |86 will become active if tube |86 had been active before.

It has been pointed out hereinbefore that the cathode circuit of tube |86 may be traced through resistances |86 and |82. Therefore when this tube is active the current in its cathode circuit produces an IR drop in resistance |88 which places the cathode at a higher positive potential than the cathode of tube 86. Therefore in a normal state with tube |66 active and tube |86 inactive the condenser |81 becomes charged with a positive potential toward the active tube. As both 'tubes are reduced to a non-conducting state by an incoming negative impulse to their suppressor grids this difference of potential disappears and ,condenser |81 discharges through resistances |88 and |89. The constants of condenser |81 are such that this discharge does not become complete by th'e time the negative impulse to the suppressor grids of the tubes terminates so that there is still a slight residual charge on condenser |61 with the upper terminal thereof at a slightly higher positive potential. This means that the rate at whichI condenser |81 discharges is slower than the rate at which the anode and cathode currents of the tubes change when the potential of their suppressor grids is lowered from zero or ground potential to a negative value controlled by the incoming negative pulse. In their normal state both' tubes are firmly -locked into 

